OBJECTIVE: To study the in vivo repair of carcinogen-induced liver DNA damage; 2) Replication of damaged DNA and 3) Their role in the initiation of chemical carcinogensis. APPROACH: Rats will be injected with hepatic and non-hepatic carcinogens. Damage in the liver DNA will be monitored by characterizing the DNA-bound carcinogen or its metabolite and analysing the size of the DNA by sedimentation in alkaline and/or neutral sucrose gradients. Repair will be followed by determining the rate of removal of DNA bound carcinogen or its metabolite and determining the size of the DNA. This type of approach will be employed to establish a relationship between the nature of the carcinogen-DNA interaction and the type of repair of such damaged DNA. Experiments will also be carried out to study the intra-genomic distribution of carcinogen binding and its subsequent removal. Replication of damaged DNA will be studied by partially hepatectomizing the rat followed by injecting H3-methylthymidine during the peak of DNA synthesis.